Method and device for network protection

ABSTRACT

The present invention relates to a protection switch in a telecommunications system. The protection switch includes at least one line driver connected to an outgoing line, at least one line receiver connected to an incoming line, a protection ring interface including an incoming link and an outgoing link to a protection ring, a line interface including said incoming and outgoing lines, a connection interface including said incoming and outgoing lines connected to a connection board, and three switches. A first switch is connected to the incoming line and to the protection ring, a second switch is connected to the outgoing line and to the protection ring, and a third switch is connected to the protection ring and to the incoming and to the outgoing lines, for re-routing traffic. The invention also relates to a method in which the protective switch is used for line protection and for equipment protection.

FIELD OF THE INVENTION

The present invention relates to a method and to a device for protectinga transmission system for protecting the system against line and boardfailures.

BACKGROUND OF THE INVENTION

It is necessary to ensure in transmission systems, such astelecommunications systems, that the signals transmitted in the systemwill arrive at the receiver, even though a standard line may be brokenor a receiving or transmitting unit is out of operation. A systemoperator accepts no losses of signals in the transmission system, andconsequently it is necessary to take precautionary measures to ensurethat the system will function faultlessly even when such faults occur Anumber of devices and methods are known to this end.

Patent Specifications U.S. Pat. No. 5,365,510, U.S. Pat. No. 5,179,548and EP-A1 677 936 teach different methods of handling cable breakages inoptical transmission systems. Briefly, the protective systems include anadditional line in the form of an optical fibre which is connectedbetween the different nodes in the system, in the same manner as thestandard line but separated physically therefrom. Communication on thespare line takes place when the standard line has broken at some placeor other. In an acute case, when the transmitter unit or receiver unitis out of function, a so-called head is formed on one side of the nodeand a so-called tail is formed on the other side of the node, therewithdisconnecting the node from the network, such that communication willcontinue between the remaining nodes in the network.

SUMMARY OF THE INVENTION

It is necessary to provide in transmission systems, and thenparticularly in telecommunications systems, some form of protectivedevice and some form of protective procedure that will ensure thatsignals transmitted in the system will always reach their intendedreceiver, irrespective of whether a line breakage occurs or if atransmitter/receiver unit stops functioning.

The present invention addresses a problem as to how this protectivedevice can be implemented in the transmission system in the cheapest andsimplest possible manner, and how the combined protection against a linefault and against a board fault can be incorporated in one and the samedevice.

The aforesaid problem is solved by means of the present invention inthat the boards which form the interface against outgoing and incominglines, the so-called line boards, include a protective switch and aremounted in a protective ring together with a stand-by unit.

Each line board includes a line driver, a line receiver and a number ofswitches. Each line board includes an associated incoming and outgoingline. These boards include the following interfaces:

an interface against its corresponding connection board, a so-calledconnection interface;

the interface against incoming and outgoing lines, the so-called lineinterface; and

an interface against the protective ring, a so-called protective ringinterface.

As before mentioned, the protective ring comprises said collection ofline boards to be protected, and a stand-by unit which is actuated inthe event of a line fault or in the event of a connection board fault.Switching to the stand-by unit can be controlled by a central monitoringunit mounted in a magazine or in the stand-by unit.

The stand-by unit includes a stand-by line board and a stand-byconnection board. A connection board forms the interface against theswitching centre or telephone exchange unit in the transmission systemand thus includes an interface against this switching centre, theso-called switching centre interface, and a further interface againstthe line board, the aforementioned connection interface.

When a fault occurs in the transmission system, the line driver willdetect the loss of signal, LOS, and can change the states of theswitches in the protection switch in coaction with the central unit,such as to switch an appropriate part of the traffic to the stand-byunit.

The protection ring may include means for transmitting a pilot tone orsome equivalent signal from the stand-by connection board, formonitoring the protection ring.

Thus, the intention of the present invention is to combine protectionagainst line faults and board faults in one single device that includesthe protection ring and the protection switches.

The present invention has the advantage of being user-friendly andflexible.

Another advantage afforded by the present invention is that it does notrequire the use of one card to remedy a line fault and another card toremedy a board fault in one and the same transmission system.

Another advantage is that the present invention does not require a spareline for each line board.

Still another advantage is that each line board in the protection ringcan be a stand-by line board.

Yet another advantage is that the protection ring can be monitored via aso-called pilot tone that will not interfere with traffic in the system.

The invention will now be described in more detail with reference topreferred embodiments thereof and also with reference to theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an inventive protection switch.

FIG. 2 illustrates a line switching centre or exchange unit interfacemodule that includes a protection ring that includes a number of lineboards in accordance with the invention.

FIG. 3 shows the line/exchange interface module with the protection ringin normal traffic.

FIG. 4 shows the line/exchange interface module with the protection ringin the case of a line fault.

FIG. 5 shows the line/exchange interface module with the protection ringin the event of a board fault.

FIG. 6 is a flowchart illustrating the start-up of the inventiveprotection ring.

FIG. 7 is a flowchart illustrating activation of the protection ring inconjunction with different types of fault.

FIG. 8 is a flowchart illustrating deactivation of the protection ringin respect of different types of fault.

DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 illustrates one embodiment of an inventive protection switch. Theprotection switch includes three switches 1, 2 and 3, a line driver 100,a line receiver 200 and a pair of amplifiers 20 and 30. The protectionswitch also includes an interface against a connection board, aso-called connection interface, an interface against a so-calledprotection ring, a so-called protection ring interface, and an interfaceagainst an incoming line 10 and an outgoing line 11, a so-called lineinterface. The protection ring interface includes a link incoming to theline board and a link outgoing from said line board. The connectioninterface and the line interface include an incoming line 10 and anoutgoing line 11.

The switches 1 and 2 are able to take two different states or positions,i.e. state a and state b. Switch 3 can take three different states orpositions, state a, state b and state c. Switch 1 is connected to theincoming line 10 and to the protection ring. Switch No. 2 is connectedto the outgoing line 11 and to the protection ring. Switch No. 3 isconnected to the protection ring, to the incoming line 10 and to theoutgoing line 11.

When switch 1 is in state a, switch 2 is in state a and switch 3 is instate a, the incoming and outgoing links in the protection ring aremutually connected, i.e. the protection ring will not influence othertraffic.

When switch 1 is in state b, switch 2 is in state a and switch 3 is instate c, the incoming link of the protection ring is connected to theincoming line 10, and the outgoing line 11 is connected to the outgoinglink of the protection ring.

When switch 1 is in an arbitrary state, switch 2 is in state b andswitch 3 is in state b, the incoming link on the protection ring will beconnected to the outgoing line 11 and the incoming line 10 will beconnected to the outgoing link on the protection ring.

The line driver 100 can either transmit on the link incoming from theprotection ring interface or on the line 11 outgoing from the connectioninterface. The line receiver 200 can either transmit on the line 10incoming to the connection interface or on the link outgoing to theprotection ring interface.

The line receiver circuit 200 is adapted to detect faults in thenetwork, Loss Of Signal, LOS. In the event of a network malfunction, forinstance a cable breakage or transmitter/receiver fault, a signal issent to the central unit and also to the line driver.

Each of the protection switches is mounted on a respective line boardbelonging to a specific incoming line 10 and a specific outgoing line11.

FIG. 2 illustrates a line/exchange interface module that includes threeconnection boards and one of the line boards from a so-called stand-byunit. The coupling boards include a so-called exchange interface. Eachof the connection boards is connected to corresponding line boards via arespective incoming line 10 and outgoing line 11. As before mentioned,the interface between the line board and the connection board is calledthe connection interface. All line boards including the stand-by unitare connected together in the protection ring. When a line breaks,either the incoming line 10 or the outgoing line 11, or atransmitter/receiver unit is out of function, this is detected by theline receiver 200 in the protection switch, wherewith said line receiversends a signal to the central unit which, in turn, orders switching fromeither the standard line board to the stand-by line board or from thestandard connection board to the stand-by connection board, depending onthe nature of the fault, ile. Whether the fault is a line fault or atransceiver fault.

FIG. 3 illustrates the line/ex change inter face module in normaltraffic, i.e. in the so-called normal state of the protection ring. Inthis state of the module, a so-called pilot tone can be sent from theconnection board in the stand-by un it so as to monitor the protectionring. When there is no fault on the protection ring, the pilot tone willreturn to the stand-by unit, whereas if there is a fault on theprotection ring, the pilot tone will not return to the stand-by unit. Afault message can be sent to the central unit to the effect that a faulthas occurred in the protection ring and that remedial action shouldtherefore be taken. The pilot tone monitoring the protection ring can besent simultaneously with other traffic on standard lines 10, 11, withoutdisturbing the traffic. The stand-by unit is constantly available as asubstitute for either the line board or the connection board. Eachconnection board and line board may be designed as a stand-by unit.

FIG. 4 shows the line/exchange interface module with a line fault at theline interface adjacent a line board, which is designated x. The lineboard x belonging to the broken line is here replaced with the stand-byline board. Traffic outgoing on the broken line then passes from thestandard connection board through the standard line board to thestand-by line board via the protection ring, and from there onto thestand-by line. Incoming traffic on the broken line is switched to thestand-by line and to the stand-by line board and through the standardline board to the standard connection board, via the protection ring.

This switching process is controlled via a central unit, which receivessignals from the line driver and line receiver of the line boardcarrying information as to which switches 1, 2, 3 shall be switched andthe states or positions to which said switches shall be switched.

FIG. 5 shows the line/exchange interface module with a transceiver faultin a connection board, here designated connection board x. The stand-byconnection board has replaced the malfunctioning standard connectionboard in the illustrated case. Traffic outgoing from the stand-byconnection board passes through the stand-by line board to the standardline board via the protection ring, and then passes out on the standardline. Incoming traffic from the standard incoming line 10 the standardline board then passes the stand-by line board via the protection ring,and from there to the stand-by connection board.

The switching process is effected via a central unit also in this case,said central unit receiving from the own monitoring of the connectionboard information signals that inform the central unit which switches 1,2, 3 shall be switched and the positions or states to which saidswitches shall be switched.

FIG. 6 is a flowchart that illustrates the protection ring start-upprocedure. The first stage of the start-up procedure is to place allswitches in the protection switch on the line board to their respectiveso-called normal states. Thus, all switches, i.e. switch 1, 2 and 3 inthe protection switch in FIG. 1, will take position a. With the switchesin this state, only the line board is connected to the protection ring.The next stage is therefore to connect the stand-by connection board tothe protection ring. This is achieved by switching switch 1 to state b,switch 2 to state a and switch 3 to state c on the stand-by line board.

Finally, monitoring of the ring is commenced by the stand-by connectionboard generating a pilot tone, or signal, having similar properties andsending the pilot tone in the closed protection ring. When no breakagesare present in the protection ring, the pilot tone will return to theconnection board. On the other hand, if the pilot tone fails to returnto the connection board, this indicates a break somewhere in the ring.

In this mode, the protection ring adopts a normal state in which thestand-by unit is constantly arranged to replace a corresponding standardboard and line, wherein monitoring of the protection ring takes place atthe same time as traffic flows on the incoming standard lines 10 and theoutgoing standard lines 11.

The procedure illustrated in FIG. 7 begins from the terminating stage inFIG. 6, i.e. the stage in which no faults were discovered and in whichthe protection ring operates in its normal state.

In the event of a fault in the protection ring, the stand-by connectionboard senses the loss of the pilot tone transmitted in the protectionring. The stand-by connection board sends to the central unit a signalto the effect that a fault has occurred in the protection ring. Thecentral unit brings to the attention of an operator the fact that afault has occurred on the protection ring and that some form of repairmust be made.

In the event of a line fault at arbitrary standard line board, which isagain designated x, that is to say a standard incoming or outgoing lineis faulty after the line board x, the line interface of the stand-byline board is connected to the protection ring. This is effected bysetting sw1 to state or position y, sw2 to state or position b and sw3to state or position b on the stand-by line board. State or position yindicates that the switch is able to take an arbitrary position orstate. The standard connection board is then connected to the protectionring, by setting sw1 in state or position b, sw2 in state or position yand sw3 in state or position c on the standard line board x. Finally, asignal to the effect that a line fault has occurred is sent from thestandard line board x to the operator, via the central unit.

In the event of a fault on the transceiver unit in any one of thestandard connection boards, which is also designated connection board x,the first step in the process is to stop monitoring of the protectionring, by switching-off the pilot tone. This is followed by updating theconfiguration data of the stand-by connection board, in other words inthe event of a fault, the central unit or some other unit having thesame function must select another traffic route. Line board x is thenconnected to the protection ring, by setting switch 1 to position orstate y, setting switch 2 to position or state b and setting switch 3 toposition or state b. Finally, there is sent to the operator an alarmsignal indicating that a fault has occurred on the connection board x inthe line/exchange interface module.

FIG. 8 is a flowchart which describes restoration to a normal statesubsequent to having repaired a ring fault, line fault or a board fault.

Once having repaired the protection ring, all that is required is for amessage to be sent to the operator to the effect that the protectionring has been restored, whereupon the operator can erase the alarm.

After having repaired a line fault adjacent the line board x or afterhaving repaired the connection board x, the operator is informed thatthe line or the connection board has been repaired. The same proceduresare then carried out, irrespective of whether the fault was a line faultor a connection board fault. The connection board x is first connectedto a standard line. The protection ring is then connected to the lineboard x, by setting switch 1 to its state or position a, setting switch2 to its state or position a and setting switch 3 to its state orposition a, i.e. setting all switches 1, 2, 3 to their respective normalstates. The stand-by connection board is then connected to theprotection ring, by setting switch 1 to its state or position b, settingswitch 2 to its state or position y and setting switch 3 to its state orposition c by the stand-by line board. Finally, the alarm to theoperator is erased.

It will be understood that the invention is not restricted to theaforedescribed and illustrated embodiments thereof, and thatmodifications can be made within the scope of the following claims.

What is claimed is:
 1. A protection switch in a telecommunicationssystem, characterized in that the protection switch is arranged with atleast one line driver connected to an outgoing line, at least one linereceiver connected to an incoming line, one protection ring interfacethat includes an incoming link and an outgoing link to a protectionring, a line interface that includes said incoming and said outgoinglines, a connection interface that includes said incoming and saidoutgoing lines connected to a connection board, and three switches, ofwhich a first switch is connected to the incoming line and to theprotection ring and of which a second switch is connected to theoutgoing line and to the protection ring and of which a third switch isconnected to the protection ring and to the incoming and the outgoingline for re-routing traffic.
 2. A protection switch according to claim1, characterized in that the line driver in the protection switch isdesigned to detect a Loss Of Signal, LOS, from different interfaces andfunctions to distinguish a line fault from a connection board fault andto set the switches (1, 2, 3) to appropriate states such as to sustainthe through-put of traffic together with a central unit.
 3. A line boardin a telecommunications system, characterized in that the line boardincludes a protection switch which has at least one line driverconnected to an outgoing line, at least one line receiver connected toan incoming line, a protection ring interface that includes an incominglink and an outgoing link to a protection ring, a line interface thatincludes said incoming and outgoing lines, a connection interface thatincludes said incoming and outgoing lines connected to a connectionboard and three switches, of which a first switch is connected to theincoming line and to the protection ring, of which a second switch isconnected to the outgoing line and to the protection ring, and of whicha third switch is connected to the protection ring and to the incomingand the outgoing line for re-routing of traffic.
 4. A line board in atelecommunications system according to claim 3, characterized in thatthe line driver in the protection switch is designed to detect Loss OfSignal, LOS, from different interfaces and is able to distinguish linefaults from connection board faults and to switch the switches (1, 2, 3)to appropriate states together with a central unit in accordance withthe detected fault, so as to maintain traffic through-put.
 5. Aprotection ring in a telecommunications system, characterized in thatthe protection ring includes at least one connection board and at leasttwo line boards which are arranged with a protection switch thatincludes at least one line driver connected to an outgoing line, atleast one line receiver connected to an incoming line, a protection ringinterface which includes an incoming link and an outgoing link to aprotection ring, a line interface which includes the aforesaid incomingand outgoing lines, a connection interface which includes said incomingand outgoing lines connected to a connection board, and three switchesof which a first switch is connected to the incoming line and to theprotection ring, of which a second switch is connected to the outgoingline and to the protection ring and of which a third switch is connectedto the protection ring and to the incoming and outgoing line forre-routing traffic, the connection-board and one of the line boardsbeing included in a stand-by unit, said stand-by unit together withremaining line boards is connected to each other in a ring.
 6. Aprotection ring according to claim 5, characterized in that the linedriver in the protection switch is designed to detect Loss Of Signal,LOS, from different interfaces and is able to distinguish a line faultfrom a connection board fault and to set the switches (1, 2, 3) toappropriate positions in accordance with the detected fault and with theaid of a central unit, so as to maintain traffic through-put.
 7. Aprotection ring according to claim 5, characterized in that theconnection board includes a connection interface against the line board,and an exchange interface against an exchange unit in thetelecommunications system.
 8. A protection ring according to claim 7,characterized in that the arrangement is such that in the event of aloss of signal from the line interface at any standard line board, theprotection switches on the line board belonging to the aforesaid lineinterface and also the protection switches on the stand-by line boardwill switch traffic from said line board to said stand-by line board viasaid switches (1, 2, 3).
 9. A protection ring according to claim 7,characterized in that the arrangement is such that in the event of aloss of signal from a connection interface at any standard connectionboard, the protection switches on the line board belonging to saidconnection board and the protection switches on the stand-by line boardwill switch traffic from said connection board to said stand-byconnection board via said switches (1, 2, 3).
 10. A protection ringaccording to claim 7, characterized in that the stand-by connectionboard is designed to transmit a pilot tone in the protection ring forthe purpose of monitoring said ring.
 11. A protection ring according toclaim 10, characterized in that the pilot tone can be transmitted in theprotection ring without disturbing standard network traffic.
 12. Amethod relating to a telecommunications system which includes at leastone connection board and at least one line board that are mutuallyconnected via an incoming line and an outgoing line, characterized byarranging the line board and a stand-by unit in a protection ring, saidline board including a protection switch; detecting in the protectionswitch a Loss Of Signal, LOS, from different interfaces mounted on theprotection switch in the event of a fault in the telecommunicationssystem; and re-routing traffic in the telecommunications system from acentral unit connected to the protection switch, by setting switchesprovided in the protection switch to a state in which faulty parts ofthe telecommunications system are replaced with necessary parts in thestand-by unit.
 13. A method according to claim 12, characterized bysetting the switches in the protection switch on the stand-by line boardin a state in which the stand-by line board is connected to theprotection ring in the event of a line fault; and setting the switchesin the protection switch on the line board belonging to the faulty lineto a state such that the connection board belonging to said faulty lineis connected to the protection ring.
 14. A method according to claim 12,characterized by stopping monitoring of the protection ring in the eventof a fault on any standard connection board; and setting the switches inthe protection switch on the line board belonging to the faultyconnection board such that said line board will be connected to theprotection ring.
 15. A method according to any claim 12, characterizedby monitoring the protection ring with the aid of a pilot tone that istransmitted in the protection ring from the stand-by connection boardand detected therefrom.